Silicone-based antifoaming agents have many superior properties to other antifoaming agents and are used in a wide variety of applications including foam-generating manufacturing steps involved in chemical, food, oil, textile, paper making, paper/pulp, and pharmaceutical industries and effluent and sewage treatments. Of the silicone-based antifoaming agents, antifoaming agents of emulsion type are commonly used which are obtained by mixing silicone oil such as dimethylpolysiloxane with finely divided silica and dispersing the oil compound in water together with a surfactant. Since the emulsion antifoaming agents are readily dispersible in foaming liquids, they exert antifoaming effect as soon as they are applied to foaming spots.
However, the emulsion antifoaming agents are so sensitive to temperature changes that problems may often arise during storage, such as compositional gradation, separation due to breaking of emulsion particles, and putrefaction. Therefore, they are unsuitable for long-term storage, with restrictions on their storage conditions.
To overcome these problems, Patent Document 1 (JP-A S60-106507) and Patent Document 2 (JP 4224535) propose powder antifoaming agents comprising antifoaming components adsorbed to oil-absorbing porous powder such as silica, aluminum oxide or talc.
However, the powder antifoaming agents having antifoaming components adsorbed to oil-absorbing porous powder such as silica, aluminum oxide or talc leave a noticeable amount of residual powder because of their composition. They are useful in effluent treatment and chemical and agrochemical industries, but not suitable in the food industry where the amount of food additives is restricted. Another drawback of the powder antifoaming agents comprising porous powder is that they are significantly inferior in water dispersibility and rapid action to the emulsion antifoaming agents.